The car passed the first half of the journey at an average speed of V1 = 20 km / h, the second

The car passed the first half of the journey at an average speed of V1 = 20 km / h, the second V2 = 10 km / h. find the average speed for the entire section.

Average travel speed:
Vav. = S / t, where S is the total distance traveled (S = S1 + S2, where S1 = 1 / 2S, S2 = 1 / 2S), t is the total travel time (t = t1 + t2).
S1 = V1 * t1, S2 = V2 * t2, where V1 = 20 km / h, V2 = 10 km / h.
Travel time when passing S1, S2:
t1 = S1 / V1 = (1 / 2S) / 20; t2 = S2 / V2 = (1 / 2S) / 10.
Let’s calculate the average speed of the vehicle:
Vav. = S / t = S / ((1 / 2S) / 20 + (1 / 2S) / 10) = S / (0.025S + 0.05S) = 1 / 0.075 = 13.3 km / h.
Answer: The average vehicle speed is 13.3 km / h.